PAB597 – A Superior Agent for the Diagnosis of BK Virus Nephropathy When Compared to SV40
Lauren E Schwartz, Jennifer Trofe-Clark, Roy D Bloom, Vivianna Van Deerlin, John Tomaszewski. Hospital of the University of Pennsylvania, Philadelphia, PA
Background: BK virus nephropathy (BKVN) is a serious post-transplant complication that almost invariably leads to graft failure in kidney transplant recipients. The gold standard for diagnosis of BKVN is histologic examination of a kidney transplant biopsy. Molecular testing for BK virus (BKV) has emerged as a valuable screening tool and management guide for BKV infection and BKVN, but has not evolved to be the gold standard for diagnosis. In most institutions an SV40 immunohistochemical (IHC) stain and/or BKV in situ hybridization (ISH) is used as an ancillary study. In recent years we have adopted the use of PAB597 IHC, a novel monoclonal antibody directed against the VP-1 capsid protein (Bracamonte E, et al, Am J Transplant 2007;7:1552-1560) to assist in the diagnosis of BKVN. In this study, we report our institutional experience with the PAB597 IHC in the evaluation of kidney transplant patients for BKVN.
Design: After IRB approval, the kidney transplant files at our tertiary care hospital were retrospectively reviewed for patients diagnosed with BKVN between January 2004 and June 2011. We reviewed a Hemotoxylin & Eosin (H&E) stained slide, IHC stained slides for SV40 and PAB597 and, when available, BKV ISH for each patient. Data points included: types of BKV inclusions seen, nuclear staining counts for SV40, PAB597 and ISH, presence or absence of cytoplasmic staining, area of tissue sections analyzed, other histologic features, BKV polymerase chain reaction (PCR) results and selected clinical information.
Results: 22 patients with a biopsy confirmed diagnosis of BKVN and histologic material available for review were identified. All patients were noted to have type 1 and/or type 2 BKV inclusions on H&E. For all 22 patients, PAB597 IHC was noted to be positive with a mean of 21 nuclear labels (NL)/mm2, whereas SV40 staining was negative for 8/22 (36%) patients (mean 12 NL/mm2). BKV PCR data was available at time of biopsy for 8/22 (36%) patients with a mean viral load value of 5.9 log copies/mL, correlating to a mean PAB597 staining level of 6.27 NL/mm2. BKV ISH was available and reviewed for 13 (59%) patients, and 12/13 showed positive staining (mean 22 NL/mm2).
Conclusions: In our experience PAB597 is a superior single reagent for the phenotypic examination of BKVN as compared to SV40. If choosing a single reagent as an ancillary study for the evaluation of BKVN, our data indicates PAB597 to be the best choice.
Category: Kidney (does not include tumors)
Wednesday, March 21, 2012 1:00 PM
Poster Session VI # 286, Wednesday Afternoon